Unloader for hydraulic pumps



Dec. 2, 1952 c. c. 5. LE CLAIR 2,619,979

UNLOADER FOR HYDRAULIC PUMPS Filed on. 1, 1947 2 SHEETS-SHEET 1 I mvenloq:

Z ZZaZI M, W, M M Wwys,

Dec. 2, 1952 c. c. 5. LE CLAIR 2,619,979

UNLOADER FOR HYDRAULIC PUMPS Filed Oct. 1, 1947 2 ,SHEETS-SHEET 2 F/GZ.

Patented Dec. 2, 1952 UNLOADER- FOR HYDRAULIC PUMPS Camille Clare Sprankling Le Clair, Acton, London, England, assignor to Tecalemit Limited, Brentford, England, a corporation of Great Britain Application October 1, 1947, Serial No. 777,326 In Great Britain October 14, 1946 11 Claims. 1

This invention relates to unloader or relief valve apparatus for use in connection with hydraulic pumps in general, and more particularly with pumps used for delivering water under high pressure such as for Washing motor vehicles and for other purposes.

Certain known unloader valves comprise a mechanical or hydraulic device, usually operated by an accumulator, such that when the quantity of liquid delivered is in excess of requirements, a suction valve is lifted and held in its raised position so that water which entersthe pump on the suction stroke is passed back again through the suction valve to a water storage tank on the delivery stroke, none being discharged to the place of use or to the accumulator.

Such unloader valves are, however, apt to cause shock since, if the apparatus functions during a discharge stroke the suction valve not only has to be lifted inwardly against the discharge pressure which is usually high, but the act of lifting it causes the pressure in the pump to be instantaneously released, giving a sudden release of stress throughout the driving mechanism.

An even worse shock takes place if, after the unloader valve has been lifted, it is closed during a discharge stroke, since this correspondingly entails an instantaneous application of stress. In the case of a multiple pump installation, at least one pump is always on its discharge stroke, so that a shock inevitably occurs every time the apparatus operates.

It is accordingly one of the objects of the present invention to provide an improved unloader valve which will operate without shock.

The unloader valve according to the present invention comprises a body having an inlet which is adapted to be connected to a pump outlet, a main outlet which is adapted to be connected to the place of use of the liquid, a subsidiary outlet for excess liquid, 9. flow-sensitive device which is movably arranged in the said body and is formed with at least one main port adapted to provide communication between the inlet and the main outlet, at least one subsidiary port which is adapted to provide communication between the inlet and the subsidiary outlet, a main valve which is adapted to open and close the said main port and thus to control the flow of liquid to the main outlet, a subsidiary valve which is. adapted to open and close the said subsidiary port and thus to control the flow of fluid to the subsidiary outlet, means connecting the two said valves to cause them to move in unison and spring means acting to hold the main valve closed, the arrangement being such that when liquid is flowing from the inlet to the main outlet and thence to the place of use the main valve in the flow-sensitive device is forced open and the said device occupies one operative position in which it holds the subsidiary valve shut, whereas when no liquid is flowing to the place of use through the main outlet the main valve automatically closes and the said device moves to a second operative position in which the subsidiary valve is open and excess liquid flows from the inlet to the subsidiary outlet.

The said flow-sensitive device is preferably slidable in the body of the apparatus and may consist of a piston which is formed with a number of main ports, the opening and closing of which is controlled by the main valve. The latter may be arranged upon a valve spindle which is slidable relatively to the piston and upon which is also mounted a subsidiary valve adapted to cooperate with a valve seat provided upon a fixed, apertured valve seat member within the said body.

The said spring means may comprise a spring which reacts between the piston and an abutmenton the valve spindle and which urges the main valve towards its closed position.

When the pump is running and no liquid is being used the main valve is closed by the action of the spring and the subsidiary valve is open. Back pressure is built up on the inlet side of the piston and a pressure equal to this back pressure is allowed to build up on the outlet side of the piston through a small throttle port or passage formed in the piston or in the body of the apparatus.

As soon as liquid is allowed to flow to the place of use, however, the pressure on the outlet side of the piston falls and the piston is displaced against the force of the spring, taking the two valves with it. As a result of this movement of the piston the subsidiary valve closes, after which the continued movement of the piston opens the main valve, thus permitting liquid to flow through the main ports in the piston, the said spring being compressed and acting to hold the subsidiary valve closed.

When the flow of liquid to the place of use is cut off the piston is moved back by the spring, thus closing the main ports through the piston. The subsidiary valve then opens, thus allowing the whole of the liquid discharged by the pump to be returned. through the subsidiary outlet to the storage tanker other container to which the subsidiary outlet is connected.

One constructional form of the invention, as applied to an unloader valve which is adapted to be fitted to a pump for supplying high pressure water to apparatus for washing. motor vehicles, will now be described, by way of example.

with reference to the accompanying drawings."

In the drawings: Figure 1 is a transverse sectional view of one form of unloader valve apparatus, constructed in accordance with the invention;-

Figure 2 is a similar view of a modification of the apparatus shown in Figure 1.

Referring first to Figure 1, the unloader valve comprises a-valve body I having a lateral inletZ which is connected to avvater pump whi'ch'is not :shown, in the drawing... The .open upper end of theabody 1is closed .by.-.a .dome-shaped cover 3 formed: witha lateral. main :outlet 6 which is connected toa water delivery pipe. or hose (not shown). This pipeorhose. isfitted with a con trol-valve=of-suitable.type at:or near the place The valve body. is also formed with a of use. 7 relief 'orsubsidiary outlet 5 located at the-bottom ofthe-.body-. This outlet is. connected-to .the'

water supply tank.

An aperture in the top of the cover 3 is thread.- ed-at 6 to receive the threaded lower end of a sleeve I which is thi'eadedinternally at its upper end to-receive a threaded, hollow closure plug .8.

The valve-body --I is-formed witha transverse partition!) which isformed centrally with an upper bosswIIl-and .with a coaxial-lower boss -I I. The two bosses are formed :with a common centrai recess -I2 andthe upper .wall of the boss I isformed as:-a machined guide I3, the purpose of which will be explained hereinafter. per boss I0 is alsoformed with a-number of lateral ports. I4, which provide communication between-the inlet 2 and the-interior of the. body above the partition-9,.on'the :one hand, and the recess- I2 and 'the space inthe. body below the partitions, onrtheother hand. I The lower face I of theboss .I I- is machined to form a flat annular seat- I for the subsidiary valve which latter will be described later;

A.-cup.-shaped piston IG with-its skirt .I'I directed downwardsztowards the partition!) is slid lowthe-piston;-I6'.- The lower. face of the boss'- I9 isemachined-ato. .form a flat seat -34--for .the main valve;aswill 'be described later.

Coaxial withthe-boss I9 is a second boss 24* extendinglupwardly-from thecrown of the piston It. This boss is of smaller diameterthanthe boss. -I9*and. is flanged at its upper end to-afford an abutment for a.- spring -2'I.- The twobosses are formedwitha common central guideway .23- the purpose of. which; will bedescribed later.

A Lthrottle' port. 12f ofsmall'diameter is also formed .throughthe crown-of the piston I6 be-v tween the boss I9 "and the skirt I1.1.

A valve spindle 22is "slidablyguidedin the The up- I aforesaid guide I3 on the partition 9 and guide 23 in the bosses of the piston IS.

The lower end of the valve spindle 22 projects below the valve seat I5 on the partition 9 and is provided with a head 25 comprising a facing and a backing washer secured byya nut. This head,'which constitutes'the subsidiary valve, is adapted to cooperate with the valve seat I5 to open and close communication between the spaces .above and below the partition 9 and thus between the inlet 2' and the subsidiary outlet 5.

The upper end of the valve spindle 22 projects upwardly through the said guideway 23 in the piston I6 this end of the spindle being threaded to receive an abutment in the form of a nut 26 which is-adjustably screwed thereon. A heavy coil spring 21 is arranged around the spindle 22 and reacts between the said boss 24 on the piston I6 and the flange 28 of a sleeve 29 which is slidably mounted on the spindle 22 below a washer .30 whichis arranged below the abutment nut 26.

A lighter spring 3! reacts between the washer. BIJ 'and a second abutment'whichiis formed by a' shoulder 32' on the closure plug 8.

The base 33A of a valve member 33 is fixedly screwed to the valve spindle 22 between theguides 23' and I3 and upon this is mounted a'disc 35 which is secured by means of screws 36;

34 with which it'cooperates, constitutes the main valve. The member 33 is formed with a skirt. 3'! through "which are cut a number of lateral ports 38 which provide communicating between the. interior of the valve body above the partition 9 and the recess I2 through'the' ports I4 inthe upper boss IE) on the partition.

The above-mentioned heavy spring 2! acts to thrust the valve spindle 22 upwards and the pis tonlfi downwards, relatively to one another, so as to force the main valve -35 in to..contact with it is not closed when the main valve islseated.

The relatively light spring 3| .urges the valve assembly bodily downwardsandlholdsi the-face of the skirt 316i the valve member. 33in contact with the face of an annular .boss..40 formed on the upper face ofthe partition-9.1Its'functioh is to prevent chattering butitisnot. essentiallto the operation of the apparatus and may. be omit-.-

ted if desired, particularly in thecase of apparatus whichis fixed .in...the pOsitionsho-wnin which the force of gravity. acting-on. the. valve T.

assembly is-generally. sufiicient for. the purpose.

In constructions in which thespringt [is omitted the sleeve 1 may beshortened. and formed with a closed end, the plug 8 being. omitted.

A'relief port 4|. formed in. the .body' I proe videscommunication-betweenthe inlet .-2 and the space in the valve 'bodybelowthenpartitionual' whichleads to the subsidiary outletiulThelower end of this relief port issurrounded-byatalve seat 43Aformed by themachined face of. abos's. 43.- A relief valve ALcooperates-with thevalve. seat QBA-and is integralwith astem. 45Lwhich" is .slidably guided in a .bore. 46 formed centrally in aclosure plugdlwhich'latter isscrewed into a threadedhole142 in the baseof the valve body; The relief valve 44 is thrust on to its seat by. a. coil spring 49 whichreacts'between the .back'of. the valve and a shoulder .50 formed upon the" plug 41.

This disc, which is larger in diameter than'the seat hose is closed, the piston I6 and the valve spindle 22, with the two valves 25 and 35 thereon, are all thrust downwards by the force of gravity and by the spring 3|, the thrust of which latter is con1- municated to the piston through the heavy spring 21. The skirt 31 of the main valve member 33 is thrust against the annular stop 60, the subsidiary valve 25 is forced off its seat and the valve seat 34 on the boss I 9 of the piston I6 is forced against the main valve 35, the longitudinal ports 25 through the piston thus being closed.

The amount of possible opening of the subsidiary valve 25 permitted by the stop 40 is such that when the water pump is started up and run at its normal speed, although the whole of the water discharged can pass through the ports 38 and I4, through the recess I2 past the subsidiary valve 25 and thus into the outlet 5, yet a certain small back pressure is built up in the space below the piston I6 in the valve body due to the resistance of these passages.

This back pressure causes a flow of water through the said throttle port H in the piston, thus permitting water to fill the space above the piston and also to fill the delivery pipe or hose attached to the main outlet 4 up to the control valve at the end of the pipe or hose. A pressure is thus built up in the space above the piston and in the said pipe or hose equal to the aforesaid back pressure. The pressure difference on the two sides of the piston thus becomes zero and the piston exerts no force in either direction, this being the normal condition when the pump is running and no water is being used.

When the control valve at the end of the delivery pipe or hose is opened, however, the pressure in the pipe or hose and in the space above the piston IE immediately falls, and the piston, under the influence of the pressure acting below it, moves upwards, taking with it by virtue of the heavy spring 21 the valve spindle 22 and the two valves 25 and 35.

The upward movement of the valve spindle first causes the subsidiary valve 25 to contact with its seat I5, thereby preventing the flow of water through the subsidiary outlet 5 and enabling the pressure in the apparatus to build up to the full working figure. The seating of the valve 25 arrests its forward movement and also the upward movement of the valve spindle 22 and the main valve 35, so that further upward movement of the piston carries it with its valve seat 34 away from the valve 35, thus causing the longitudinal ports 25 to open and permitting the discharge of water to the place of use. This further movement of the piston I5 compresses the spring 21, the strength of which is sufficient to hold the valve 25 in contact with its seat I5 against the full working pressure of the apparatus.

The subsidiary valve 25 can only be held on its seat by virtue of the upward thrust exerted upon it by the piston through the heavy spring 21, and this thrust can only be produced by a difierence of pressure above and below the piston.

Thus, if the eifective diameter of the piston is six times the effective diameter of the subsidiary valve 25, its area thus being thirty-six times the area of the valve, the pressure difference across the piston will be one thirty-sixth of the pressure of the valve. In other words, one thirty-sixth or approximately 3% of the pressure provided by the pump is lost in the apparatus and does not reached the place of use of the water. Thus, it is necessary to adjust the pump pressure to 3% above the required working pressure.

When the said control valve on the hose is closed the further flow of water through the longitudinal ports 25 in the piston is arrested. Almost immediately the pressures above and below the piston will be equalised and the piston will consequently descend under the influence of the spring 21 until the valve seat 34 contacts the main valve 35, thus closing the longitudinal ports 20. Thereafter, the piston I6 and the spindle 22 will descend in unison under the influence of the spring 3I and/ or gravity and the subsidiary valve 25 will again be moved off its seat.

After the control valve on the hose has been closed and before the valve 25 can open to its designed amount, however, it is necessary for the piston to move an appreciable distance, first to close the ports 28' and then to open the valve 25. During the latter part of this motion the speed of movement of the piston is limited by the speed at which water can pass through the throttle port 2| to fill the void which would otherwise form in the space above the piston, Hence an appreciable delay must occur between the closing of the control valve and the opening of the subsidiary valve 25. During this delay pressure within the apparatus might build up to a dangerous level and cause damage to the apparatus and injury to persons in the vicinity. Such a rise of pressure is prevented by the opening of the relief valve 44 which provides temporary communication between the inlet 2 and the subsidiary outlet 5.

The lowering of the valve 25 then opens full communication between the inlet 2 and the subsidiary outlet 5, thus permitting the whole of the pump discharge to return to the storage tank, as previously explained. As soon as this occurs the relief valve 44 will close again.

The working pressure of the apparatus is determined by adjusting the compression of the spring 21 by means of the said threaded abutment nut 25 on the valve spindle 22. This is so adjusted that when the piston I6 with its valve face 34 is moved away from the main valve 35 and the longitudinal ports 29 through the piston are opened, as previously explained, the thrust on the spring 21 is suihcient to hold the subsidiary valve on its seat against the full working pressure of the pump which, as stated previously, is slightly in excess of the pressure delivered to the place of use.

Figure 2 of the drawings shows a modified form of unloader valve which incorporates various improvements over the valve shown in Figure 1, although the principle of operation is fundamentally the same in the two constructions.

Referring to Figure 2 the valve comprises a body IQ! which is formed with an integral cover I53 and is closed at its lower end by means of a removable base cover IEO, the whole forming a chamber for the valve mechanism and being formed with an inlet I52, with a main outlet I04 and with a subsidiary outlet I55, these inlets and outlets corresponding to the inlets and outlets 2, 4 and 5, respectively, of Figure l.

A partition plate I09, the edges of which are clamped between the body I Ill and the base cover Hid, divides the interior of the body into upper and lower chambers which communicate with each other by means of a central port I I i formed in the partition I59. partition H39 it is formed with an annular rim or boss I I l, the lower edge of which is machined to form a valve seat II5.

A piston [I5 having a skirt II'I, which parts correspond to the piston IE and skirt I1 of Figure On the underside of the A cap Ii'tI isv screwed intothe lower open end of theskirt III,

which is flanged inwardly -andformed with a 1,

thread! I52 for this purpose.

formed-with a projectingcentrally-bored boss I 53 T whi'eh provides a guide for -the lower end-f a valve spindle 'I22. The upper end ot-this'spindle isenla'rged at I54 andi's slidable in a guideway I23 formed'in the crown oi-the-piston 'I I6; 1

The lower end of the valve-"spindle-I22 below the cap IEI is-redu'cedin-diameter and-passes through the port I Idin' the partition lfie and carries a subsidiary valve head "I259 This valve 1 head is provided with-a removable facing washer I55 which is adapted to engage on thevalveseat. I IE to close the port I I-t when the spindle I I2 is moved upwardly.

'Iheheadof the piston II6 is formed with an internal -*conical-boss-- I I 9, thelower end of which I is'machined to form'an annularvalve sea-t I3'4'-.- This-seat surrounds the lower end of an enlarged bore I56-which isformed in the boss' I le below the guidewayi233 This'bore 455 is connected withthe'space-above the piston by means of a number of inclined'ports I2I bored through the head ofthe piston.

The valve spindle 222 is threaded immediately function of the disc of Figural, isprovided'on' the upper face of the flange I53 ofthe sleeve I51 and cooperates with the valve seat I34. This constitutesthe'main valve and controls the flow of liquid from the space within the piston lit to the space above the latter. piston'is in free communication with the space below the cap IEI by means of a series of ports I59-whichare formed through the flange at the bottom of the skirt I I1 around the cap I5I.

Two concentric compression springs I27 and IZ'IA *are'arranged between the flange I58 and the cap IEI at'the bottom of the piston. This cap I5 I-is screwed into the inwardly turned flange on the piston skirt II! by means of the thread I52 until the springs I27 and [21A are given the de sired'compression; whereafter the cap I5I is locked in position by means of a locking wire I68 which is passedthrough holes drilled-in'the cap 5! and in theflange of the piston skirt;

It'will be apparent that the parts of'the apparatus'so far described correspond operationally to those parts shown in Figure 1 which bear corresponding reference-numbers. Thus the piston IIG corresponds to the piston I6,-the main valve I35 with its seat I34 correspond to the valve 35 andseat 3 !,whil the subsidiary valve I25 and its seat=I t5 correspond to the subsidiary valve The interior of the- 325 with its seat- I 55' The main valve I35 controls the flow of liquid from the inlet IE2 and the space below the piston, via= the ports I59, the

interior cfthe pistonand the ports I20,to the-- main-outlet 5%. Similarly the subsidiary valve I25 controls the fiow'of liquid from the inlet I02 through the port I I4 tothe subsidiary outlet I 05.

In;the construction of Figure 2,however, there a throttle port correspondingto the port 2|, the

functions of this port being fulfilled by-a throttle passage which is formed in the wall of the body IOI. This passage comprises-a vertical passage IBI which leads'fromthe inlet- I02, atiits lower ,duced .diameter.

end, to. a horizontal: bore I 62: also formed win the body III I, at its upper end, the inner end of: this i bore I62 being connected -withxtheinterior ofthe body- IIJI by-meansof a threaded bore Ifit 'oirea A jet member 7 I 64 which '-'is.

formed with a jet orifice I65,- is screwedintothe bore I 53; To facilitate the insertion and removal of the member I64 it'i's-formed with a flange 466 i" which is slotted to receive'a'screw-driver-or ure;

tool. The outer end of thebore I62 is closed by=- means of a screw plug I6-I- which can be removed when access isirequired to thijet member.

The effective size-of the-throttle passage is'determined by the size-of the-jet orifice-I65} To' vary this it'is only necessary to remove the-m'em-' ber- I64-and to replace: it by a :similar member having an orifice of a different: size.

In-order to prevent the flow of water through the inlet I02 past [the -lower-end of the throttle" passage I6I from exerting any suction-effect? which upset the operation of the apparatus,--thelower part of the passage-Whisenlarged as shown at I68.- If desired the-whole-passage-could bemade of the same diameter as the part" I682"- The location of the throttle passage-in thewall of the body instead of'in the'piston'as previously described-has the advantage that it enables the eiTective-size-of the throttle passage to be readily adjusted-as required to obtain the best results; without having to dismantle the apparatus:-

Theconstruction shown -irr Fi-g; 2 is also provided-with a relief valve I44, which *fulfils'exactly the same function as the-valve= 44 of Figure 1.

In this case, however,the valve M4" is shown-as being of tubular form, being slidablewithin' a hollow valve seat member I43which' is screwed-into a threaded bore formed in the lower part of the body IUI.

The lower end I69 of the seat member I43 forms a seatagainst whicha flange I10 on the valve member I i-4 is-adapted to engage: A 1 spring I49 acts on the valve I44 to urge-it into its upper or closed position, the lower-end of the spring being contained in and bearing against the bottom of a recessed cover. I4I'which"is' screwed into the bottom of. the base I001 thence to the subsidiary outletIUBf A Ithreaded bor I13 Jm'ay be provi'dedinthe" top of the casing, if desired, for the connection of a pressure gauge.

The modified-form of unloader valve shown in-- Figure 2 operates in a similar manner to that de' scribed with reference to Figure 1 and its opera-ii tion will be clear from ,the foregoing-description takenin conjunction withthe drawings,

I claim:

1. Un'lo'adervalve apparatu comprisin'g.abody having an .inletjadapted to be connected tola pump outlet, a main outlet adaptedcto -be..con

nected .to the place of use of-the. .liquid a subsidiary outlet for excess liquid, means dividing, said-body into. a pairioflspaces so that. said inlet; and said main outlet communicatewith .the firsti.

space and said subsidiary outlet. communicates with l the second 1 space,-.. a flow sensitive device movably mounted-in saidvfir'sttspace andiposie. V tioned between said inletand said =main outlet and having at least r0116. main port adapted :to 7 provide communication between saidinlet and said main outlet and a main valve seat at said port, at least one subsidiary port in said dividing means adapted to provide communication between said first space and said second space and therefore betweensaid inlet and said subsidiary outlet, a main valve member which by cooperation with said main valve seat is adapted to open and close said main port and to control the flow of liquid between said inlet and said main outlet, a subsidiary valve member to open and close said subsidiary port and to control the flow of liquid to said second space and said subsidiary outlet, means interconnecting said valve members to cause them to move in unison so that when one port is closed the other port is open, and spring means urging said main valve member to port closing position, so that when liquid under pressure is flowing from said inlet to said main outlet said main port is opened by the liquid pressure in said first spac moving said flow sensitive device to a first operative position wherein said subsidiary valve member is moved to closed position and when no liquid flows through said main outlet due to excessive back pressure thereat said main port is automatically closed and said flow sensitive device is moved to a second operative position wherein said subsidiary valve member is moved to open position and excess liquid flows from said inlet through'said first space through said subsidiary port to said second space and said subsidiary outlet.

2. Unloader valve apparatus as claimed in claim 1 wherein a cylinder is formed in said first space and said flow sensitive device comprises a piston slidabl in said cylinder.

3. Unloader valve apparatus comprising a body having an inlet adapted to be connected to a pump outlet, a main outlet adapted to be connected to the place of use of the liquid, a subsidiary outlet for excess liquid, means dividing said body into a pair of spaces so that said inlet and said main outlet communicate with the first space and said subsidiary outlet communicates with the second space, a cylinder formed in said first space, a flow sensitive piston positioned between said inlet and said main outlet slidable in said cylinder, said piston having at least one main port adapted to provide communication between said inlet and said main outlet and a main valve seat at said port, at least one subsidiary port in said dividing means adapted to provide communication between said first space and said second space and therefore between said inlet and said subsidiary outlet, a main valve member which by cooperation with said main valve seat is adapted to open and close said main port and to control the flow of liquid between said inlet and said main outlet, a subsidiary valve member to open and close said subsidiary port and to control the flow of liquid to said second space and said subsidiary outlet, a common valve spindle slidably guided relative to said piston and interconnecting said valve members to cause them to move in unison so that when one port is closed the other port is open, an abutment carried by said spindle, and spring means reacting between said piston and said abutment to move said main valve member to port closing position, so that when liquid under pressure is flowing from said inlet to said main outlet said piston is moved to a first position to open said main port and to close said subsidiary port and when no liquid flows through said main outlet due to excessive back pressure thereat said piston is moved to a second operative position wherein it closes said main port and opens said subsidiary port and excess liquid flows from said inlet through said first space through said subsidiary port to said second space and said subsidiary outlet.

4. Unloader ,valve apparatus as claimed in claim 3 including means for adjusting the position of said abutment on said valve spindle to adjust the spring loading.

5. Unloader valve apparatus comprising a body having an inlet adapted to be connected to a pump outlet, a main outlet adapted to be connected to the place of use of the liquid, a subsidiary outlet for excess liquid, a partition dividing said body into a pair of spaces so that said inlet and said main outlet communicate with the first space and said subsidiary outlet communicates with the second space, a flow sensitive device movably mounted in said first space and positioned between said inlet and said main outlet and having at least one main port adapted to provide communication between said inlet and said main outlet and a main valve seat at said port, a subsidiary port in said partition to-provide communication between said first space and said'second space and therefore between said inlet and said subsidiary outlet, a main valve member which by cooperation with said main valve seat is adapted to open and close said main port and to control the flow of liquid between said inlet and said main outlet, a subsidiary valve member to open and close said subsidiary port and to control the flow of liquid to said second space and said subsidiary outlet, a valve spindle siidably guided relative to said flow sensitive deice and said partition and interconnecting said valve members to cause them to move in unison so that when one port is closed the other port is open, and spring means urging said main valve member to port closing position, so that when liquid under pressure is flowing from said inlet to said main outlet said main port is opened by the liquid pressure in said first space moving said flow sensitive device to a first operative position wherein said subsidiary valve member is moved to closed position and when no liquid flows through said main outlet due to excessive back pressure thereat said main port is automatically closed and said flow sensitive device is moved to a second operative position wherein said subsidiary valve member is moved to open position and excess liguid flows from said inlet through said first space through said subsidiary port to said second space and said subsidiary outlet.

6. Unloader valve apparatus as claimed in claim 5, including means associated with said valve spindl and engageable with said partition for lie iting the opening movement of said subsidiary valve member.

'7. Unloader valve apparatus comprising a body having an inlet adapted to be connected to a pump outlet, a main outlet adapted to be connected to the place of use of the liquid, :a subsidiary outlet for excess liquid, means dividing said body into a pair of spaces so that said inlet and said main outlet communicate with the first space and said subsidiary outlet communicates with the second space, a flow sensitive device movably mounted in said first space and posi tioned between said inlet and said main outlet and having at least one main port adapted to provide communication between said inlet and said main outlet and a main valve seat at said port, a throttle port by-passing said flow sensitive device and adapted to equalize the liquid pressure on opposite sides of said flow sensitive w-ztofopen and :close said main port and tozcontrol the flow of liquid between said-inlet and" said m-ainoutlet, a subsidiary valve member-to open a and close -said-subsidiary*portiand tov control the flow of'liquid to "said-second space and'said rsu-bsidiary 'outlet,- means interconnecting -.said

valve members to cause them to move inunison so that when one port is closed the other-port isvopen;andspring means urgingsaid main valve member .to port closing position, so that when -the liquid pressure at-- said main outlet is re- :rduced said main-port is opened by the unbalance ofuliquid- "pressure between said: inlet and.- said fi-main outlet movin said flow "sensitive device to a first operative position wherein said subsidiary valve member is moved :to closed position and -When no -liquid flows through said' main outlet ,dueto excessive back pressure thereat said main p port is automatically closed andsaid flow sensiwtive device-is moved to second operative position -z-whereinsaidsubsidiary valve member is -moved vtry-open position andexcess liquid flowsfrom said ?inlet through said first space through said subsidiary port to said second space and said subsidiary outlet.

- 8.- Unloader' valve apparatus 2 as claimed in rrclaim- 7iwherein"said throttleport is formed in 1'saidvfiowsensitivedevice tQvDI'QVidG communication =between2 the r-opposite sides .thereof.

9.;Unloader rvalve' apparatus .--asclaimed in V lclaim 7' wherein a cylinder: is formed in-saidifirst spacepsaid flow-sensitive devicecomprises a piston -slidable .in-said: cylindenrand said throttle port is formed in said rpistonrtoeprovideconstant communication between the opposite sides thereof to equalize thevpressure-on both sides thereof when said main port isclosed.

- -10; Unloader valve apparatus .as "claimed." in

-::.claim '7- Whereinsaid-throttle port. is .formeduin a i throttle passage formedi. said valve body aroundsaid flow sensitive device.

-11.- Un1oader valve. apparatus xasQclaimedJn I claim 7 including a throttlesformed.invsaidvalve body around said fiOW'mSenSitiVe 111931115, said throttle port. being v f orined ,by1 a .jet lremovably mounted insaidipassage.

1 CAMILLE CLARE ISPRANKLINGALE CLAIR.

s REFERENCES. CITED The" following -references are ot-record in'Zthe fileof 'this patent:

1 UNITED STATES PATENTS "Number Name .,-Date .1;052,172 Rateau -4 Feb.-,4,: 1913 1,199,152 '1 Bruce septa- 26; -1-916 1,215,071 Steedman Feb; V6, 1917 1,421,309 Redfield -T--June:27,w1922 902,231 Gurley m Mar-s 21; 1933 

